The present invention relates broadly to plastic, i.e., polymeric, flexible tubing bundle constructions, and more particularly to flame retardant multi-tube bundle constructions principally for optical fiber cable installation applications.
Flexible tubing bundles of the type herein involved are used in a variety of instrumentation, control, sensing, and fluid transfer applications as shown, for example, in U.S. Pat. Nos. 5,563,975; 5,392,374; 4,653,541; and 2,578,280, and in the publications xe2x80x9cParflex Multitube(copyright) Instrumentation and Heat Trace Tubing Products,xe2x80x9d Catalog 4200-M-1/USA, May 2000, Parker Hannifin Corporation, and xe2x80x9cFutureFlex(copyright) Systems Innovative Cable Product Catalog,xe2x80x9d Sumitomo Electric Lightwave Corp. In basic construction, such bundles involve an inner bundle of high density polyethylene, nylon, or other plastic tubing, and an outer cover or jacket which surrounds the bundle. Electrical wires, optical fiber cables, and other signally devices typically are received through the each of the tubes in the bundle which thereby provide a means both for the routing of the devices through an installation and for segregating different groupings of those devices. Depending upon the requirements of the particular application or installation, one or more intermediate layers of fiber, tape, foil, or plastic may be extruded, wrapped, knitted, woven, or otherwise provided between the jacket and the tubing bundles as a physical reinforcement and/or for thermal or electrical insulation or flame resistance.
Indeed, flame retardancy is of particular importance in the case of tubing bundles for optical fiber cables or other signaling devices intended for vertical installation within a plant, building, or other facility. In this regard, without some degree of flame retardancy, there can exist in a fire situation the potential for flame to propagate vertically along the tubes in the bundle to adjacent floors in the structure. Accordingly, tubing bundles intended for vertical installations generally must comply, in the U.S. and elsewhere, with certain codes, standards, or other regulations, most commonly Underwriter""s Laboratories (UL) Standard No. 1666, xe2x80x9cTest for Flame Propagation Height of Electrical and Optical-Fiber Cables Installed Vertically in Shafts.xe2x80x9d As a result, it is believed that tubing bundles constructions meeting, particularly, UL 1666 would be well-received by, among others, the optical fiber cable market.
The present invention is directed to flexible plastic, i.e., thermoplastic, tubing bundle constructions, and particularly to a flame retardant multi-tube construction which is particularly adapted for installations of optical cables or other signaling devices. In one arrangement, the construction includes an innermost thermal transfer layer which surrounds the tubing bundle and thereby provides for the conduction of heat way from the tubes to thereby minimize the ignition thereof and the resultant potential, particularly in a vertical installation, to propagate the fire in a flame environment. A fire-resistant layer is provided to surround the thermal transfer layer to further insulate the tubes to maintain the temperature thereof below their ignition or combustion temperature. The fire-resistant layer also functions to maintain the mechanical integrity of the construction in a fire situation and otherwise to retard flame penetration into the tubing bundle. Advantageously, the tubing bundle construction of the present invention is believed would meet UL 1666 requirements without the necessity to provide an innermost thermoplastic layer which is intended to intumescence or liquefy and then to char as a means of providing a fire stop barrier.
In an illustrative embodiment, the tubing bundle construction includes at least one and, typically, a plurality of high density or molecular weight polyethylene, nylon, or other plastic tubes arranged in a bundle. An innermost layer of an aluminum or other metal foil tape, or other thermally-conductive material, is spiral or otherwise wrapped over the tube bundle, preferably in an overlapping, spiral fashion, with a fire-resistant layer of an aramid fiber or other fire-resistant tape being spiral wrapped over the metal foil layer. Optionally, a polyester or other film tape may be spiral or otherwise wrapped over the fire-resistant tape as a moisture and vapor barrier layer, with a jacket formed of a flame-retardant polyvinyl chloride or other thermoplastic or plastic being extruded or wrapped over the vapor barrier layer.
The present invention, accordingly, comprises the construction, combination of elements, and arrangement of components which are exemplified in the detailed disclosure to follow. Advantages of the present invention include a flexible tubing bundle tubing construction which is particularly adapted for vertical optical fiber cable installations, and which is believed would comply with UL 1666 requirements. Additional advantages include a tubing bundle construction which is economical to manufacture. These and other advantages will be readily apparent to those skilled in the art based upon the disclosure contained herein.